The invention relates to a contact element for arrangement between two base contact parts to be connected to one another with electrical conduction.
Such a contact element has at least two strips and a row of webs which are arranged between said strips, cohesive with these and twisted with respect to them and are springy and normally form elongated lamellae and which touch contact surfaces of the two base contact parts and can thus connect them conductively to one another, said contact surfaces facing one another and being a distance apart. Such contact elements can be used in particular for electrical connecting apparatuses in which relatively large currents, for example at least 20 A, are to be transmitted from one base contact part to another base contact part. The two base contact parts are normally separable from one another. The contact element is normally detachably held on one of the two base contact parts and, for example, frequently arranged in a groove inside the base contact part.
The distance between the contact surfaces to be connected to one another may vary within a certain range owing to manufacturing inaccuracies, especially in many connecting apparatuses--for example in connecting apparatuses serving as plug connectors or switches. The webs of a contact element should therefore be highly springy and in particular have a sufficient spring travel in order to be able to compensate the tolerance interval of the distance between the contact surfaces.
Various known contact elements consist of a piece of tape having two edge strips running along the tape edges and a row of twisted webs which are arranged between said edge strips and are cohesive with these and which form elongated lamellae, are at right angles to the edge strips and have a middle section which is connected to each of the two edge strips by a constricted part. In the known contact elements, the opposite edges of webs following one another along the web row are separated from one another over their entire length by slits, even when said webs are in the untwisted state. Furthermore, the contact elements are formed, for example, from sheet metal which consists of a copper-beryllium alloy strip, has been hardened by a heat treatment after shaping and has silvered surfaces.
For example, German Patent 1,665,132 discloses a contact element which has two parallel, straight edge strips and webs which are separated from one another by slits and whose two edges in the region of the middle section are arc-shaped and curved with mirror symmetry relative to one another. To ensure that the elongated webs of this known contact element have sufficient springiness, they must have a certain minimum width at right angles to their longitudinal directions. The minimum width is dependent on the distance between the opposite contact surfaces of the two base contact parts. Since slits are also present between the successive webs, the grid spacing, i.e. the distance, measured along the web row, between corresponding points of adjacent webs, is furthermore even greater than the stated minimum width of the webs. The known contact elements therefore have relatively few webs based on a length unit measured in the longitudinal direction of the web row, and permit only a correspondingly small current transmission per stated length unit.
To avoid this disadvantage, German Patent 2,243,034 envisages gathering the contact elements by making their edge strips wavy and/or meander-shaped, the edge strips preferably overlapping in certain sections. However, such a shaping of the edge strips requires additional tools and operations. Since the wavy or meander-shaped edge strips have very small radii of curvature or even folds, after hardening of the contact elements the edge strips are more likely to break during use of the contact elements. It is true that this danger of breakage can be reduced by making the edge strips flexible again after hardening by heat treatment. However, this requires additional operation which makes production of contact elements more expensive, so that such contact elements are substantially more expensive than contact elements having nonwavy edge strips. In addition, in the heat treatment which serves to make the edge strips flexible, it is virtually impossible to prevent hose sections of the webs close to the edge strips from partially losing their hardness and hence their spring effect, which is likewise disadvantageous.
Furthermore, the edge strips which are wavy or meander-shaped according to German Patent 2,243,034 have, in a longitudional section, a height which is substantially greater than the material thickness of the contact element. This may make it necessary for any grooves provided for holding the contact elements to be deeper than in the case of contact elements having smooth, nonwavy edge strips. Moreover, instead of swallowtail grooves frequently used for holding contact elements, it may be necessary to provide grooves of different shape.